Organic electroluminescent device

ABSTRACT

This invention relates to a borane derivative represented by the formula (1) and an organic electroluminescent device:                    
     wherein R 1  to R 8  and Z 2  are each independently a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryloxy group; X, Y and Z 1  are each independently a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, an alkoxy group or an aryloxy group; substituents of Z 1  and Z 2  may be united to form a condensed ring; and n is an integer of 1-3; with the provisos that when n is two or more, Z 1 s may be different from each other; and that cases where n is 1, X, Y and R 2  are each methyl, and R 8  is hydrogen or substituted boryl and those where n is 3 and Z 1  is methyl are excluded. The borane derivatives of this invention are suitable for luminescent materials by virtue of their high luminous efficiencies in solid states, and useful for electrophotography and as photoelectronic functional materials including nonlinear optical materials and conductive materials. The use of this borane derivative brings about an organic EL device characterized by low electricity consumption and high efficiency.

This application is a 371 application of PCT/JP99/07219 filed Dec. 22,1999.

TECHNICAL FIELD

The present invention relates to novel borane derivatives, variousmaterials and organic electroluminescent devices (hereinafter referredto as “organic EL device”) comprising the borane derivatives.Specifically, this invention relates to borane derivatives having novelstructures, and various materials and organic EL devices comprising theborane derivatives having the structures, which are useful as electronicfunctional materials and optical functional materials.

BACKGROUND ART

Various institutions have tried to apply π electron type organiccompounds to optical functional materials and electronic functionalmaterials in various ways.

Among them, borane compounds which intramolecularly contain boron atomshave unique optic and electronic properties probably owing to theexistence of the empty p orbital of the boron atom. However, the boranecompounds have generally been unsuitable for the use as such materials,because of their instability to air and water.

With respect to such a problem, it has been reported that the boranecompound can become stable to air and water when constituted so as to bebulky, namely, when introducing bulky substituents around a boron atomso as not to expose the boron atom outward. Thus it is highly likelythat the borane compound having such a structure can apply for nonlinearoptical materials and organic EL devices.

Examples of borane compounds stable in the air have been reported in J.Chem. Soc. Chem. Commun., 1998, 963 (hereinafter referred to as Document1), J. Am. Chem. Soc., 120, 10776(1998) (hereinafter referred to asDocument 2), and J. Am. Chem. Soc., 120, 5112 (1998) hereinafterreferred to as Document 3). Further, applications of borane compounds tononlinear optical materials have been reported in Appl. Organomet.Chem., 10, 305(1996) (hereinafter referred to as Document 4). Inaddition, an application of borane compounds to organic EL devices hasbeen reported in J. Am. Chem. Soc., 120, 9714 (1998) (hereinafterreferred to as Document 5).

Documents 2 and 3 describe the maximum fluorescent wavelength, but thedescriptions are limited to the luminescence property in solution state.There is no description on the luminescence property in solid statewhich is actually used in such application. Further, the structuresdisclosed are limited to polymers, and there is no description on anylow molecular weight compounds.

Document 4 also describes the fluorescent property in the solutionstate, but there is neither description about the luminescence in thesolid state, nor description about applications for the luminescentmaterials.

Thus the studies have not been made sufficiently for using the “bulky”borane compound in any substantial applications at present.Particularly, there has been a demand to apply the borane material tothe organic EL devices. Many studies have been made in order to findsuch a compound as the device, which has not led to any satisfactoryresult yet.

The organic EL device essentially comprises a structure wherein anorganic compound as a charge transport material and/or a luminescentmaterial is sandwiched in between two electrodes. The highly efficientorganic EL device of a low power consumption is required, and thus it isnecessary to select an organic compound of high luminous efficiency asthe luminescent material.

Document 5 describes some borane compounds such as5,5′-bis(dimesitylboryl)-2,2′-(bithiophene) and5,5″-bis(dimesitylboryl)-2,2′:5′,2″-(terthiophene) used for electrontransport materials (charge transport materials), but does not mentiontheir luminescence property or suitability for luminescent materials.This literature merely mentions the device comprising the boranecompound having a lower current density, i.e., a more improved luminousefficiency, than that of the device of the same luminance not comprisingthe borane compound.

JP-A 7-102251 also describes an example of the boron compound used forthe organic EL device. However, this boron compound requires a highvoltage for driving the device, and has a low luminance.

Since there are few literatures on the luminescence property of boranecompounds, any highly efficient organic EL device of a low powerconsumption has not been prepared by using borane compounds known as araw material for the organic EL device. Therefore, there has been ademand for a borane compound having a specific structure effective as amaterial for an organic EL device.

DISCLOSURE OF THE INVENTION

The present inventors have made intensive studies in order to provide anew borane derivative, and various materials and organic EL devices eachcomprising the borane derivative. As a result, the inventors have foundthat a borane derivative having a specific structure, and a material,particularly an organic EL device, comprising the borane derivative cansolve the above-mentioned problems, whereby the present invention havebeen achieved.

The present invention is described below in detail.

The borane derivative of the present invention is a new compoundrepresented by the following formula (1). The present borane derivativeis expected to be used in a wide variety of applications such aselectronic functional materials and optical function materials takingadvantage of electronic properties originating from the borane atom, aswell as for luminescent materials and charge transport materials.

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3;

with the provisos that when n is two or more, Z₁s may be different fromeach other; and that cases where n is 1, X, Y and R₂ are each methyl,and R₈ is a hydrogen atom or substituted boryl and those where n is 3and Z₁ is methyl are excluded.

Among the borane derivatives represented by the formula (1), preferableare those wherein at least one substituted or unsubstituted 9-anthrylgroup is bonded to the boron atom.

Concrete examples of the borane derivative according to this inventioninclude the compounds represented by the following formulae (3) to (9).

The compound represented by the formula (3) is one of the boranederivatives of the above formula (1) wherein n is 3, R₄ to R₈ are eachhydrogen atom, and Z₁ and Z₂ are benzo-condensed.

The compound represented by the formula (4) is one of the boranederivatives of the above formula (1) wherein n is 3, R₄ to R₇ are eachhydrogen atom, one R₈ is a dianthrylboryl group and the other two R₈sare each hydrogen atom, and Z₁ and Z₂ are benzo-condensed.

The compound represented by the formula (5) is one of the boranederivatives of the above formula (1) wherein R₄ to R₇ are each hydrogenatom, R₈ is phenyl, n is 3, and Z₁ and Z₂ are benzo-condensed.

The compound represented by the formula (6) is one of the boranederivatives of the above formula (1) wherein n is 2, R₁ and R₃ to R₈ areeach hydrogen atom, R₂, X and Y are each methyl group, and Z₁ and Z₂ arebenzo-condensed.

The compound represented by the formula (7) is one of the boranederivatives of the above formula (1) wherein n is 2, R₁ and R₃ to R₇ areeach hydrogen atom, R₂, X and Y are each methyl group, one R₈ isanthrylmesitylboryl, the other R₈ is a hydrogen atom, and Z₁ and Z₂ arebenzo-condensed.

The compound represented by the formula (8) is one of the boranederivatives of the above formula (1) wherein n is 3, R₄ to R₈ are eachhydrogen atom, Z₁ and Z₂ are benzo-condensed at one position, the othertwo Z₁s not condensed are a methyl group, and the other two Z₂s notcondensed are a hydrogen atom.

The compound represented by the formula (9) is one of the boranederivatives of the above formula (1) wherein n is 1, R₁ and R₃ to R₇ areeach hydrogen atom, R₂, X and Y are each methyl group, R₈ is a phenylgroup, and Z₁ and Z₂ are benzo-condensed.

The borane derivative, which is used as various materials according tothis invention, namely, luminescent materials, charge transportmaterials and materials for organic EL devices (luminescent layer,charge transport layer), is represented by the following formula (2):

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3; with the proviso that when nis two or more, Z₁s may be different from each other.

The borane derivative preferably has a “bulky” structure so as to bestable even in the air and to show enough durability and performance assuch a material. The borane derivative preferably has an anthracene ringand/or a naphthalene ring.

Therefore, the luminescent material, charge transport material andorganic EL device of this invention preferably comprise the boranederivatives represented by the formula (2), wherein at least onesubstituted or unsubstituted 9-anthryl group is bonded to a boron atom.

Concrete examples of such a borane derivative include the compoundsrepresented by the following formulae (10) to (14), in addition to thoseof the aforementioned formulae (3) to (9).

The borane derivative according to this invention and the boranederivative used for the materials according to this invention(hereinafter abbreviated as “the borane derivative of this invention”for convenience) may be synthesized by various known methods including atypical synthesis shown below. Specifically, the borane derivative ofthis invention can be obtained by the reaction of the compoundrepresented by the following formula (15) with a base, followed by thereaction with a borane compound.

ArW  (15)

wherein Ar denotes the following formula (16) or (17), and W is ahalogen atom.

wherein R₁ to R₃ are each independently a hydrogen atom, a saturated orunsaturated hydrocarbon group, an aromatic group, a heterocyclic group,a substituted amino group, a substituted boryl group, an alkoxy group oran aryloxy group; and X and Y are each independently a saturated orunsaturated hydrocarbon group, an aromatic group, a heterocyclic group,a substituted amino group, an alkoxy group or an aryloxy group; and

wherein R₄ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; and Z₁ is a saturated orunsaturated hydrocarbon group, an aromatic group, a heterocyclic group,a substituted amino group, an alkoxy group or an aryloxy group; or Z₁and Z₂ may be united to form a condensed ring.

The base to be used in this method includes, for example, organolithiumreagents such as n-butyl lithium, tert-butyl lithium and phenyl lithium,and magnesium reagents such as magnesium and magnesium bromide. Thesolvent to be used is not particularly limited and any solvent may beused as far as it is inert to the base used. In general, ether solventssuch as diethyl ether and tetrahydrofuran (hereinafter abbreviated as“THF”), and aromatic solvents such as benzene and toluene may be used.The borane compound to be used includes halogenated boranes such astrichloro borane, trifluoro borane, and complexes thereof; and alkoxyboranes such as trimethoxy borane and triisopropoxy borane.

The reactions as mentioned above are preferably carried out in an inertgas such as nitrogen and argon gas. The reaction temperature is notparticularly limited but usually and preferably in the range of −78° C.to 120° C. The reaction time is not particularly limited also, and thereaction may be stopped when the reaction sufficiently progressed. Thereaction may be confirmed by a conventional analytical means such as NMRand chromatography, and the end of the reaction may be determined at theoptimum point in the analysis.

The borane derivatives of this invention may also be obtained bysubstitution reaction of the compound obtained by above-mentionedmethod. The substituent to be added to the compound by the substitutionmay include alkyl groups such as methyl, ethyl, n-propyl, isopropyl,cyclopentyl and tert-butyl; alkenyl groups such as vinyl, allyl, butenyland styryl; alkoxy or aryloxy groups such as methoxy, ethoxy, propoxyand phenyloxy; amino groups such as dimethylamino and diphenylamino;silyl groups such as trimethylsilyl, dimethyl-tert-butyl silyl,trimethoxysilyl and triphenylsilyl; boryl groups such as dianthrylboryland dimesitylboryl; aryl groups such as phenyl, naphthyl, anthryl,biphenyl, toluyl, pyrenyl, perylenyl, anisyl, terphenyl andphenanthrenyl; and heterocyclic groups such as hydrofuryl, hydropyrenyl,dioxanyl, thienyl, furyl, oxazolyl, oxadiazolyl, thiazolyl,thiadiazolyl, acridinyl, quinolyl, quinoxalinyl, phenanthrolinyl,benzothienyl, benzothiazolyl, indolyl, silacyclopentadienyl and pyridyl.

In addition, these substituents may form a ring structure by bonding toeach other at any site in the compound.

The organic EL device according to this invention essentially has astructure wherein a borane derivative layer comprising the boranederivative represented by the formula (2) as a main component issandwiched in between a pair of electrodes (anode and cathode).

The borane derivative is suitable as a material for both a luminescentlayer and a charge transport layer (hole injection layer, hole transportlayer, electron injection layer and electron transport layer), becauseit can be used as both a luminescent material and an electron injectionmaterial. The borane derivative layer thus obtained effectively acts asa luminescent layer and a charge transport layer.

The borane derivative layer may further comprise any of hole injectionmaterials, hole transport materials, luminescent materials, electroninjection materials and electron transport materials in addition to theborone derivative of this invention.

The organic EL device may comprise an electron-donating compound and anelectron-accepting compound, which are added in admixture or laminated,as a charge transport material in many cases. It is known that thesecompounds form unfavorable charge-transfer complex or exciplex. However,the borane derivatives of this invention has a structure in which“bulky” substituents bonded to a boron atom are propeller-like locatedaround the boron atom, and therefore, it is difficult to form thecharge-transfer complex or exciplex in this compound. Accordingly, thehighly efficient element can advantageously be obtained, when usingborane derivatives for the organic EL device as the electron-donatingcompound or electron-accepting compound.

The organic EL device according to this invention may optionallycomprise any additional layers such as hole injection layers, holetransport layers, luminescent layers, electron injection layers,electron transport layers and interlayers, in addition to the boranederivative layer, between the electrodes.

The following are concrete examples of the organic EL device of thisinvention having laminated structures:

(1) anode/borane derivative layer/cathode;

(2) anode/hole injection layer/borane derivative layer/cathode;

(3) anode/borane derivative layer/electron injection layer/cathode;

(4) anode/hole injection layer/borane derivative layer/electroninjection layer/cathode;

(5) anode/hole injection layer/borane derivative layer/electrontransport layer/interlayer/cathode;

(6) anode/hole injection layer/hole transport layer/borane derivativelayer/electron injection layer/cathode; and

(7) anode/hole injection layer/hole transport layer/borane derivativelayer/electron injection layer/interlayer/cathode.

Although hole injection layers, electron injection layers, holetransport layers, electron transport layers and interlayers are notalways essential in this invention, they improve the luminousefficiency. Particularly, the hole injection layer and the holetransport layer significantly improve the luminous efficiency.

The organic EL device according to this invention is preferablysupported on the substrate. Any substrate may be used as far as it hassufficient mechanical strength, thermal stability and transparency.Glass and transparent plastic film, etc. may be cited as examples.

Anode materials used for the anode of the organic EL device of thisinvention include metals, metal alloys, electrically conductivecompounds and mixtures thereof, which have a work function of more than4 eV. Metals such as Au and electroconductive transparent materials suchas CuI, indium tin oxide (hereinafter referred to as “ITO”), SnO2 andZnO may be cited as examples.

Cathode materials used for the cathode of the organic EL device of thisinvention include metals, metal alloys, electrically conductivecompounds and mixtures thereof, which have a work function of less than4 eV. Calcium, magnesium, lithium, aluminum, magnesium alloy, lithiumalloy, aluminum alloy, and mixtures of aluminum/lithium,magnesium/silver and magnesium/indium, etc. may be cited as examples.

In this invention, the light transmittance of at least one electrode ispreferably not less than 10% so as to efficiently obtain the lightemission from the organic EL device. The sheet resistance as anelectrode is preferably not more than several hundred Ω/mm. The filmthickness depends on the property of electrode materials, but it isusually selected within a range of 10 nm to 1 μm, and preferably 10-400nm. Such electrodes may be manufactured by a method such as vapordeposition and sputtering wherein a thin film is formed using theabove-mentioned electrode material (anode material and cathodematerial).

The luminescent layer as an essential layer of the organic EL device ofthis invention preferably comprises the borane derivatives representedby the aforementioned formula (2). However, any luminescent materialsother than the borane derivatives of this invention may be used. It isalso possible to use the mixture of the borane derivatives of theformula (2) and other luminescent material in order to obtain a lightwavelength different from that of the borane derivative, or to enhancethe luminous efficiency. Further, there is no problem in using two ormore borane derivatives of the formula (2) in combination.

The luminescent materials other than the borane derivatives of theformula (2) may include various known materials such as daylightfluorescent materials mentioned in “Optical Function Materials”,Functional Polymer Material Series, Society of Polymer Science, Japaned., Kyoritsu Shuppan Co., Ltd. (1991), p. 236, optical whiteningagents, laser dyes, organic scintillators, various fluorescence analysisreagents.

Specifically, preferred are polycyclic condensation compounds such asanthracene, phenanthrene, pyrene, chrysene, perylene, coronene, rubreneand quinacridone; oligophenylene compounds such as quarterphenyl;scintillators for the liquid scintillation such as1,4-bis(2-methylstyryl)benzene, 1,4-bis(4-methylstyryl)benzene,1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene,1,4-bis(5-phenyl-2-oxazolyl)benzene,2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene,1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1,3,5-hexatriene and1,1,4,4-tetraphenyl-1,3-butadiene; metal complexes of oxine derivativesdisclosed in JP-A 63-264692; coumarin dyes; dicyanomethylene pyran dyes;dicyanomethylene thiopyran dyes; polymethine dyes; oxobenzanthracenedyes; xanthene dyes; carbostyril dyes and perylene dyes; oxazinecompounds disclosed in Germany Patent No. 2534713; stilbene derivativesdisclosed in the 40th Japan Applied Physics Related Association LectureProc., 1146 (1993); spiro compounds disclosed in JP-A 7-278537; andoxadiazoles disclosed in JP-A 4-363891.

The hole injection layer, which is an optional layer of the organic ELdevice of this invention, can be prepared by using the hole injectionmaterial. The hole injection layer may be prepared as a single layercomprising one or more hole injection materials or as multiple holeinjection layers comprising various hole injection materials.

The hole transport layer, which is an optional layer of the organic ELdevice of this invention, can be prepared by using the hole transportmaterial. The hole transport layer may be prepared as a single layercomprising one or more hole transport materials or as multiple holetransport layers comprising various hole transport materials.

The hole injection material and the hole transport material may comprisethe borane derivatives of the formula (2), but it is also possible touse any material which has been conventionally used as a chargetransport material for an positive hole in a photoconductive material,or any known material which can be used for hole injection layers orhole transport layers of the organic EL devices.

Concrete examples of such known materials include, for example,carbazole derivatives (e.g., N-phenyl carbazole, polyvinyl carbazole,etc.); triarylamine derivatives (e.g., TPD, polymers having an aromatictertiary amine in its principal chain or its side-chain,1,1-bis(4-di-p-tolylaminophenyl)cyclohexane,N,N′-diphenyl-N,N′-dinaphthyl-4,4′-diaminobiphenyl (hereinafterabbreviated as “NPD”),4,4′,4″-tris{N-(3-methylphenyl)-N-phenylamino}-triphenylamine, compoundsdisclosed in Journal of the Chemical Society, Chemical Communication, p.2175 (1996), compounds disclosed in JP-A 57-144558, JP-A 61-62038, JP-A61-124949, JP-A 61-134354, JP-A 61-134355, JP-A 61-112164, JP-A4-308688, JP-A 6-312979, JP-A 6-267658, JP-A 7-90256, JP-A 7-97355, JP-A6-1972, JP-A 7-126226, JP-A 7-126615, JP-A 7-331238, JP-A 8-100172 andJP-A 8-48656, and star-burst amine derivatives described in AdvancedMaterial, Vol. 6, p. 677 (1994), etc.), stilbene derivatives (thosedisclosed in 72nd CSJ (the Chemical Society of Japan) National Meeting,Lecture Proc. (II), p. 1392, 2PB098, etc.); phthalocyanine derivatives(non-metal, copper phthalocyanine, etc.); and polysilanes.

The electron injection layer, which is an optional layer of the organicEL device of this invention, can be prepared by using the electroninjection material. The electron injection layer may be prepared as asingle layer comprising one or more electron injection materials or as amultiple electron injection layer comprising various electron injectionmaterials.

The electron transport layer, which is an optional layer of the organicEL device of this invention, can be prepared by using the electrontransport material. The electron transport layer may be prepared as asingle layer comprising one or more electron transport materials or as amultiple electron transport layer comprising various electron transportmaterials.

The electron injection material and the electron transport materialpreferably comprise the borane derivatives of the formula (2), but it isalso possible to use any material which has been conventionally used asan electron transfer compound in a photoconductive material, or anyknown material which can be used for electron injection layers orelectron transport layers of the organic EL devices.

Concrete examples of such known materials include, for example,diphenylquinone derivatives (those disclosed in Journal of the Societyof Electrophotography of Japan, 30, 3 (1991), etc.), perylenederivatives (those described in J. Apply. Phys., 27, 269 (1988), etc.),oxadiazole derivatives (those disclosed in the above mentioned Lit.,Jpn. J. Appl. Phys., 27, L713 (1988), and Appl. Phys. Lett., 55, 1489(1989), etc.), thiophene derivatives (those disclosed in JP-A 4-212286,etc.), triazole derivatives (those disclosed in Jpn. J. Appl. Phys., 32,L917 (1993), etc.), thiadiazole derivatives (those disclosed in PolymerPreprints, Japan, Vol. 43, No. 3 (1994), (III) Pla007, etc.), metalcomplexes of oxine derivatives (those disclosed in Technical Report ofInstitute of Electronics, Information and Communication Engineers, 92(311), 43 (1992), etc.), polymers of quinoxaline derivatives (thosedisclosed in Jpn. J. Appl. Phys., 33, L250 (1994), etc.), andphenanthroline derivatives (those disclosed in Polymer Preprints, Japan,Vol. 43, No. 7 (1994), 14J07, etc.)

Hole injection materials, hole transport materials, luminescentmaterials and electron injection materials, which are usable in theorganic EL device of this invention, preferably have a Tg of not lessthan 80° C., more preferably not less than 100° C.

Preferable interlayers, which are optional layers of the organic ELdevice of this invention, are those which can promote the injection ofthe electron from the cathode, and those which can prevent the positivehole from flowing into the cathode. These are selected according to thecompatibility with the material used for the cathode. Lithium fluoride,magnesium fluoride, calcium fluoride, etc. may be cited as concreteexamples.

Each layer constituting the organic EL device of this invention may beprepared by forming the material for constituting the layer into a thinfilm by any known method such as vapor deposition, spin coating andcasting.

The film thickness of each layer formed by such a method is notparticularly limited, and it can be properly determined depending uponproperties of the material used. It is usually selected within the rangeof 2 nm to 5000 nm.

When the vapor deposition method is used to form the material into athin film, the depositing conditions may be varied depending on the kindof the borane derivatives, the crystalline structure and the associatedstructure of the intended molecular built-up film. In general, it ispreferably selected within the following ranges: the boat heatingtemperature of 50 to 400° C., vacuum of 10⁻⁶ to 10⁻³ Pa, deposition rateof 0.01 to 50 nm/sec., substrate temperature of −150 to +300° C., andfilm thickness of 5 nm to 5 μm.

Next, the method of manufacturing the organic EL device, which has theaforementioned structure (1) comprising anode/borane derivativelayer/cathode, is explained as an example of the method for producingthe organic EL device of this invention.

A thin film comprising an anode material is formed on an adequatesubstrate by the vapor deposition method so as to be 1 μm or less,preferably 10 to 200 nm, in thickness. Then, a thin film of the boranederivative is formed onto the resulting anode layer to obtain aluminescent layer. A thin film comprising a cathode material is formedonto the luminescent layer by the vapor deposition method so as to be 1μm or less in thickness, resulting in a cathode layer. The desiredorganic EL device is thus obtained.

Alternatively, the order of manufacturing the above-mentioned organic ELdevice can be reversed, namely, the cathode, the luminescent layer andthe anode may be produced in order.

When applying a DC voltage to the resultant organic EL device, it may beapplied with the anode set to a positive polarity and the cathode set toa negative polarity. If applying a voltage of approximately 2 to 40 V,the light emission can be observed from the transparent orsemi-transparent electrode side (anode or cathode, and both).

This organic EL device can emit lights as well when applying an ACvoltage. Any waveform of the AC may be applied.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention shall specifically be explained withreference to the following examples, but this invention shall not belimited thereto.

Synthesis of Borane Derivatives

EXAMPLE 1 Synthesis of the Compound of the Formula (4)

13 ml of a hexane solution of n-butyl lithium (1.6 mol/l) was added to30 ml of an ethereal solution containing 5.14 g of 9-bromoanthracene at−78° C. under argon flow. The temperature was then raised to 0° C. andthe reaction mixture was stirred for 30 minutes. Subsequently, themixture was added to 10 ml of an ethereal solution containing 4.1 ml ofboron trifluoride at that temperature and the solution was stirred for 1hour to yield a precipitate as a yellow solid.

The supernatant was then removed and 30 ml of dry ether was added to theprecipitate. After stirring for 1 hour, the supernatant was againremoved and 30 ml of dry THF was added.

Further, an ethereal solution of 9,10-dilithioanthracene was addeddropwise to the solution, which was stirred for 3 hours at roomtemperature. Precipitates were removed by filtration and the filtratewas concentrated. Ethyl acetate was added to the concentrate and theprecipitate was recrystallized from ethyl acetate to yield the desiredcompound (4% yield). This compound emitted red fluorescence in a solidstate.

¹H-NMR (C₆D₆): δ=6.41 (dd, 4H), 6.77 (t, 8H), 7.06 (t, 8H), 7.77 (d,8H), 8.35 (s, 4H), and 8.59-8.63 (m, 12H).

EXAMPLE 2 Synthesis of the Compound of the Formula (6)

The title compound was synthesized according to the method as describedin Example 1, except that 9,10-dilithioanthracene was replaced bymesityl lithium.

¹H-NMR (C₆D₆): δ=2.0 (s, 6H), 2.10 (s, 3H), 6.71 (s, 2H), 6.91 (t, 4H),6.88-6.94 (m, 4H), 7.06-7.12 (m, 4H), 8.35 (s, 2H), and 8.49 (d, 4H).

EXAMPLE 3 Synthesis of the Compound of the Formula (3)

13 ml of a hexane solution of n-butyl lithium (1.6 mol/l) was added to30 ml of an ethereal solution containing 5.14 g of 9-bromoanthracene at−78° C. under argon flow. The temperature was then raised to 0° C. andthe reaction mixture was stirred for 30 minutes. Subsequently, themixture was added to 10 ml of an ethereal solution containing 0.8 ml ofboron trifluoride at that temperature and the solution was stirred for12 hour to give a precipitate as an orange solid.

The precipitate was recrystallized from benzene to yield the desiredcompound (33% yield).

¹H-NMR (C₆D₆): δ=6.83-6.89 (m, 6H), 7.21 (t, 4H), 7.95 (d, 6H), 8.12 (d,6H), and 8.58 (s, 4H).

Preparation of Organic EL Devices and Properties Thereof

EXAMPLE 4

ITO was deposited in a thickness of 100 nm on a glass substrate (25mm×75 mm×1.1 mm) (manufactured by Tokyo Sanyo Vacuum Co., Ltd.) by avapor deposition method, which was used as a transparent supportsubstrate. This transparent support substrate was fixed in a substrateholder of a commercially available vapor deposition apparatus(manufactured by Sinku Kiko Co., Ltd.), which was equipped with a quartzcrucible containing N,N′-dinaphtyl-N,N′-diphenylbenzidine (hereafterabbreviated as “NPD”), a quartz crucible containing the compound of theformula (10), a quartz crucible containing1,1-dimethyl-2,5-bis{2-(2-pyridyl)pyridyl}-3,4-diphenylsilacyclopentadiene(hereafter abbreviated as “PYPY”), a graphite crucible containingmagnesium and a graphite crucible containing silver.

The vacuum chamber was evacuated to 1×10⁻³ Pa, and then the cruciblecontaining NPD was heated so that NPD could be vapor-deposited to have afilm thickness of 50 nm, thus forming a positive hole transport layer.Next the crucible containing the compound of the formula (10) was heatedso that the compound could be vapor-deposited to have a film thicknessof 15 nm, thus forming a luminescent layer. Further, the cruciblecontaining PYPY was heated so that PYPY could be vapor-deposited to havea film thickness of 35 nm, thus forming an electron transport layer. Therate of vapor deposition was each 0.1 to 0.2 nm/sec.

Subsequently, the vacuum chamber was evacuated to 2×10⁻⁴ Pa, and thenthe graphite crucibles were heated to deposit magnesium at a depositionrate of 1.2 to 2.4 nm/sec, and simultaneously, to deposit silver at adeposition rate of 0.1 to 0.2 nm/sec. A 150-nm alloy electrode ofmagnesium and silver was formed on the organic layer, whereby an organicEL device was obtained.

The ITO electrode was used as an anode and the alloy electrode ofmagnesium and silver as a cathode. When a DC voltage was appliedthereto, a current of about 1 mA/cm² flowed and green light having abrightness of about 100 cd/m² and a wavelength of 515 nm was emitted.

COMPARATIVE EXAMPLE 1

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced bytris(8-hydroxyquinoline)-aluminum.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 1 mA/cm² flowed and green light having abrightness of about 20 cd/m² and a wavelength of 522 nm was emitted. Theemission brightness was lowered to about one-fifth as compared with thatobtained in Example 4.

COMPARATIVE EXAMPLE 2

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by trimesitylborane.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 50 mA/cm² flowed and purple light having abrightness of about 5 cd/m² was emitted. The emission brightness and theemission efficiency were lowered to a great extent as compared withthose obtained in Example 4.

EXAMPLE 5

A device was prepared according to the method as described in Example 4,except that PYPY was not used and that the thickness of the layercomprising the compound of the formula (10) was changed to 50 nm.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 1 mA/cm² flowed and green light having abrightness of about 6 cd/m² and a wavelength of 515 nm was emitted.

EXAMPLE 6

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by thecompound of the formula (4).

The ITO electrode was used as the anode and the alloy electrode made ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 1 mA/cm² flowed and red light having abrightness of about 6 cd/m² and a wavelength of 616 nm was emitted.

EXAMPLE 7

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by thecompound of the formula (11).

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 1 mA/cm² flowed and blue light having abrightness of about 30 cd/m² and a wavelength of 464 nm was emitted.

EXAMPLE 8

The transparent support substrate used in Example 4 was fixed in thesubstrate holder of the vapor deposition apparatus, which was equippedwith a quartz crucible containing NPD, a quartz crucible containing thecompound of the formula (10), a tungsten crucible containing aluminumand a tungsten crucible containing lithium fluoride.

The vacuum chamber was evacuated to 1×10⁻³ Pa, and then the cruciblecontaining NPD was heated so that NPD could be vapor-deposited to have afilm thickness of 50 nm, thus forming a positive hole transport layer.Next the crucible containing the compound of the formula (10) was heatedso that the compound could be vapor-deposited to have a film thicknessof 50 nm, thus forming an electron-transporting luminescent layer. Therate of vapor deposition was each 0.1 to 0.2 nm/sec.

Subsequently, the vacuum chamber was evacuated to 2×10⁻⁴ Pa, and thenthe tungsten crucibles were heated so that lithium fluoride could bevapor-deposited to have a film thickness of 2 nm on the organic layerand finally aluminum could be vapor-deposited to have a film thicknessof 100 nm on the organic layer, whereby an organic EL device wasobtained.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 2 mA/cm² flowed and green light having abrightness of about 100 cd/m² and a wavelength of 515 nm was emitted.

EXAMPLE 9

A device was prepared according to the method as described in Example 8,except that the compound of the formula (10) was replaced by thecompound of the formula (4).

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 2 mA/cm² flowed and red light having abrightness of about 15 cd/m² and a wavelength of 616 nm was emitted.

EXAMPLE 10

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by thecompound of the formula (9).

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 2 mA/cm² flowed and blue light having abrightness of about 100 cd/m² and a wavelength of 477 nm was emitted.

EXAMPLE 11

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by thecompound of the formula (12).

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 0.7 mA/cm² flowed and green light having abrightness of about 100 cd/m² and a wavelength of 511 nm was emitted.

EXAMPLE 12

A device was prepared according to the method as described in Example 4,except that the compound of the formula (10) was replaced by thecompound of the formula (13).

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 30 mA/cm² flowed and red light having abrightness of about 100 cd/m² and a wavelength of 622 nm was emitted.

EXAMPLE 13

The transparent support substrate used in Example 4 was fixed in thesubstrate holder of the vapor deposition apparatus, which was equippedwith a quartz crucible containing NPD, a quartz crucible containing thecompound of the formula (10), a quartz crucible containing the compoundof the formula (11), a quartz crucible containing PYPY, a tungstencrucible containing aluminum and a tungsten crucible containing lithiumfluoride.

The vacuum chamber was evacuated to 1×10⁻³ Pa, and then the cruciblecontaining NPD was heated so that NPD could be vapor-deposited to have afilm thickness of 50 nm, thus forming a positive hole transport layer.Next the crucible containing the compound of the formula (10) and thecrucible containing the compound of the formula (11) were heated so thatthe compounds could be vapor-deposited to have a film thickness of 15nm, thus forming a luminescent layer. Further, the crucible containingPYPY was heated so that PYPY could be vapor-deposited to have a filmthickness of 35 nm, thus forming an electron transport layer. In thisprocess, the composition ratio of the respective compounds was 2% of thecompound of the formula (10) to 98% of the compound of the formula (11).

Subsequently, the vacuum chamber was evacuated to 2×10⁻⁴ Pa, and thenthe tungsten crucibles were heated so that lithium fluoride could bevapor-deposited to have a film thickness of 0.5 nm on the organic layerand aluminum could finally be vapor-deposited to have a film thicknessof 100 nm on the organic layer, whereby an organic EL device wasobtained.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 1 MA/cm² flowed and bluish green lighthaving a brightness of about 100 cd/m² and a wavelength of 495 nm wasemitted.

EXAMPLE 14

A device was prepared according to the method as described in Example13, except that the compound of the formula (10) was replaced by thecompound of the formula (14) and that the compound of the formula (11)was replaced by tris(8-hydroxyquinoline)aluminum.

The ITO electrode was used as the anode and the alloy electrode ofmagnesium and silver as the cathode. When a DC voltage was appliedthereto, a current of about 20 mA/cm² flowed and red light having abrightness of about 100 cd/m² and a wavelength of 600 nm was emitted.

INDUSTRIAL APPLICABILITY

The borane derivative, the new compound of the present invention has ahigh luminescence efficiency in a solid state and is therefore suitablefor a luminescent material. It is also useful for electrophotography andas photoelectronic functional materials such as nonlinear opticalmaterials and conductive materials.

Further, the organic EL device of the present invention contains aluminescent material having a high luminescent efficiency, andtherefore, it can provide a display having a low power consumption and along life.

What is claimed is:
 1. An organic electroluminescent device comprising aborane derivative represented by the following formula (2):

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3; further wherein when n istwo or more, Z₁s may be different from each other.
 2. The organicelectroluminescent device according to claim 1, having a luminescentlayer which comprises one borane derivative represented by the formula(2) or a mixture of two or more borane derivatives represented by theformula (2), or a mixture of at least one borane derivative representedby the formula (2) and at least one luminescent material other than theborane derivatives represented by the formula (2).
 3. The organicelectroluminescent device according to claim 1, having a chargetransport layer which comprises the borane derivative represented by theformula (2).
 4. The organic electroluminescent device according to claim1, wherein the borane derivative is a compound wherein at least onesubstituted or unsubstituted 9-anthryl group is bonded to the boronatom.
 5. The organic electroluminescent device according to claim 2,wherein the borane derivative is a compound wherein at least onesubstituted or unsubstituted 9-anthryl group is bonded to the boronatom.
 6. The organic electroluminescent device according to claim 3,wherein the borane derivative is a compound wherein at least onesubstituted or unsubstituted 9-anthryl group is bonded to the boronatom.
 7. An organic electroluminescent device comprising at least ananode, a cathode and a luminescent layer interposed therebetween, theluminescent layer comprising a borane derivative represented by thefollowing formula (2):

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3, further wherein when n istwo or more, Z₁s may be different from each other.
 8. The organicelectroluminescent device according to claim 7, wherein the boranederivative is a compound wherein at least one substituted orunsubstituted 9-anthryl group is bonded to the boron atom.
 9. Theorganic electroluminescent device according to claim 7, furthercomprising a charge transfer layer.
 10. The organic electroluminescentdevice according to claim 9, wherein the charge transfer layer comprisesa borane derivative represented by the following formula (2):

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3, further wherein when n istwo or more, Z₁s may be different from each other.
 11. A method ofproducing electroluminescence comprising providing a luminescentmaterial and applying voltage across the luminescent material so thatthe luminescent material can exhibit electroluminescence, wherein theluminescent material comprises a borane derivative represented by thefollowing formula (2):

wherein R₁ to R₈ and Z₂ are each independently a hydrogen atom, asaturated or unsaturated hydrocarbon group, an aromatic group, aheterocyclic group, a substituted amino group, a substituted borylgroup, an alkoxy group or an aryloxy group; X, Y and Z₁ are eachindependently a saturated or unsaturated hydrocarbon group, an aromaticgroup, a heterocyclic group, a substituted amino group, an alkoxy groupor an aryloxy group; substituents of Z₁ and Z₂ may be united to form acondensed ring; and n is an integer of 1-3; further wherein when n istwo or more, Z₁s may be different from each other.